1. Field of the Invention
The present invention relates to contact lenses. In particular, the invention provides a method for designing a contact lens, prescribing a contact lens based upon the design method, the use of a wavefront sensor to carry out such methods, and contact lenses obtained by these methods.
2. Description of Related Art
Contact lenses come in many forms: soft, RGP, monofocal, multifocal, diffractive, alternating style, simultaneous style, and more. They provide correction for various vision problems including myopia, hyperopia, astigmatism, presbyopia, and others.
Typical contact lens design involves designing the lens"" physical parameters, such as posterior surface curvature over the optical and transition zones, anterior surface curvature, surface shapes, thickness, and others, based on the need for each parameter to fit the cornea in an appropriate fashion, namely, to center over the pupil, to move appropriately with blinking, to provide an acceptable level of comfort to the wearer, and to provide the necessary optical correction of vision. These parameters, particularly surface curvatures, are usually derived by a combination of experience or historical data gathered from the performance of previous designs, and empirical xe2x80x9ctrialxe2x80x9d fittings and testing of the new design on a sample of intended patients. Based upon the subjective response of the patients and observations by the fitter, the design may be altered to achieve the intended outcome.
In consideration of the foregoing, the inventors have recognized a need for, and advantages resulting from, an improved method for designing contact lenses based upon objective criteria, and for providing contact lenses based upon the improved design. The inventive methods allow the design parameters of the lens to be chosen which provide an optimized optical correction. Lenses provided according to the invention will result in better optical performance in-situ, encompassing the effects created by placing the lens on the eye.
An embodiment of the invention is directed to an improved method for designing a contact lens. An aspect of this embodiment involves the steps of determining an objective measurement criteria of optical performance of a contact lens in-situ, determining a technique for measuring this criteria, determining a lens design parameter (for a constant refracting power) that can be varied to induce a change in the optical performance of the lens in-situ, measuring the in-situ optical performance of a test lens over a range of different design parameter values, and selecting the design parameter value for designing a contact lens that gives a desired in-situ optical performance measurement. Objective, in-situ optical performance is preferably determined by a retinal image metric such as, e.g., the point spread function (PSF), modulation transfer function (MTF), Strehl ratio, and others well understood in the art. The preferred technique for measuring this criteria is the use of a wavefront sensor (aberrometer) to obtain real-time wavefront aberration information. The preferred design parameters are physical design parameters such as the shape of the posterior lens surface, the shape of the anterior lens surface, and/or the asphericity of the anterior lens surface. Alternatively, the design parameter may be an optical parameter such as the higher-order aberration content of the lens, e.g., the amount of spherical aberration of the lens. The design parameter may alternatively be in the form of a lens factor that induces a higher-order aberration in the patient""s eye. Most preferably, the and described in detail below, and defined in the appended claims, involves making test lens measurements on a statistically significant population group. The preferred design parameter will then coincide with the best objectively measured optical performance determined by statistical analysis. The design method thus allows the lens designer to develop contact lenses that will provide the best optical performance for the largest cross section of contact lens wearers.
Another embodiment according to the invention relates to a method for providing a contact lens that delivers improved in-situ optical performance. An aspect of this embodiment involves the steps of obtaining a subject""s manifest refraction and prescribing an appropriate contact lens designed according to the design method set forth herein. In a related aspect, a method is described for fitting an individual with an optimized contact lens. In this method, the subject is fitted with a first trial lens having the appropriate refractive power and a first design parameter value. The optical performance of the test lens is objectively measured in-situ, and the subject is again fitted with a second test lens of the appropriate power having a different value of the respective design parameter. Another measurement is then obtained. This process is repeated as desired, and the lens that provides the optimum optical performance (in consideration of comfort and other factors) can be prescribed and dispensed to the patient.
In another embodiment according to the invention, a method for using an aberrometer for designing and prescribing a contact lens includes making a wavefront measurement of a subject""s eye with a first in-situ trial lens having a known design parameter value that affects optical performance, making another wavefront measurement of the subject""s eye with another in-situ trial lens having a respective design parameter of a different value, monitoring an objective optical performance metric of each trial lens based upon the respective wavefront measurements, and designing or prescribing a contact lens based upon the design parameter of the trial lens that provided the optimum optical performance metric.
The methods and apparatus according to the invention are embodied in various types and styles of contact lenses including, but not limited to, a soft monofocal lens, a soft multifocal lens, an RGP monofocal lens, an RGP multifocal lens, a toric lens, simultaneous style presbyopia correcting lenses, alternating vision style presbyopia correcting lenses, and diffractive lenses.
The stated objects and advantages of the invention, and others, will be further appreciated in view of the description and drawings that follow, and by the appended claims which define the invention.